1. Field of the Invention
The present invention relates to an equipment used for manufacturing a semiconductor device and, more particularly, to an equipment for sticking an adhesive tape on a semiconductor wafer (referred to simply as a "wafer" hereinafter).
2. Description of the Prior Art
As well known in the art, one wafer contains a number of semiconductor chips (or pellets or dice) and hence the wafer is required to be diced to obtain individual semiconductor chips. At this time, in order to prevent the individual chips from being scattered, the wafer is stuck with an adhesive tape or sheet made of, for example, vinyl chloride and then diced into the individual chips. An equipment for sticking an adhesive tape of a wafer (called hereinafter "tape sticking equipment") is thus required.
A conventional tape sticking equipment includes a wafer support stage having a uniformly flat surface on which a semiconductor wafer is placed with a front side thereof being in contact with the support stage. The front side of the wafer contains a plurality of circuit elements such as transistors, resistors and so on. An adhesive tape is then stuck on the backside surface of the wafer by turning a roller with a pressure. Thus, the compressing force of the roller presses the whole front side of the wafer against the wafer support stage. Because of this, when the thickness of the wafer is nonuniform or when a slight unevenness exists on the surface of the wafer, stresses tend to concentrate locally on the wafer, so that there arise damages in the wafer itself or in the crystal structure of the wafer. Moreover, if there exists foreign materials on the surface of the support stage, the damage of the wafer is further enhanced, resulting in a substantial reduction in the yield.
In order to solve the above drawbacks, there is disclosed in Japanese Patent Laid Open No. 62-287639 and Japanese Patent Laid Open No. 63-166243 a tape sticking equipment in which a wafer support stage is constructed to have a recessed part to support only the peripheral part of a wafer and a gas is sent with a high pressure into a hollow portion formed between the recessed part of the wafer support stage and the wafer. In accordance with such an equipment, the major front side of the wafer is free from being in direct contact with the support stage. Moreover, the flexure in the wafer caused by the pressurization of the roller can be prevented by sending the gas with the pressure so as to cancel or counteract the pressure of the roller.
However, in that case, the pressure of the gas thus sent is applied to the entire surface of the wafer. Recently, the wafer is becoming large in the diameter and small in the thickness. For these reasons, when the roller is on the peripheral edge portion of the wafer, the balance in the pressure between the roller and the gas is destroyed and the latter pressure prevails over the former. As a result, the wafer is warped convexly to bring about a distortion in the crystal structure of the wafer. In the worst case, the wafer is broken.
In view of this, it is conceivable to vary the internal pressure of the hollow portion of the support stage in accordance with the position of the roller. To this end, however, it is required to detect the internal pressure and accordingly control the pressure of the gas to be sent, so that the tape sticking equipment is made complicated and expensive.